Energy Optimization in grinding circuits A proces perspective.pptx

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1. Energy Optimization in Grinding Circuit A Process Perspective Day in day out , construction sites all around the world can count on Mapei Jaleel Mohamed – Technical Sales Manager - Cement Additives 7 May 2024

2. 2 Decarbonization in cement Industry Efficiency Improvement: Process Bottlenecks Optimization Thermal efficiency Precise control Fuel Substitution: Remove and replace fossil fuel Including Hydrogen Including Electricity New Cement composition : Reduced clinker content New cementitious materials Incl . Calcined Clay Incl . Recycled Concrete Carbon Capture: Technology Storage or Usage

3. 3 Safety awareness ! Key learning: Appropriate PTW and WPRA for the activities. Follow the LOTO (Lockout & Tagout) procedure. Ensure materials were drained out or emptied out from the process circuits. Positivity isolation of rotating equipments.

4. 4 Electrical Energy consumption in cement Industry Communition section Kwh/t of Clinker Crushing 1- 2 Grinding of rawmeal 15 -25 Grinding of raw coal 2 - 4 Grinding of Cement 30 - 60 Total Communition 45 - 85 Total Power consumption 90 - 130

5. 5 Types of grinding circuits Specific energy consumption, kWh/t For blended cement with Blaine 3600, 85% clinker, 5% gypsum, 10% limestone Sp. Power Kwh/t of cement Ball mill CCBM RP Pregrinder + Ball mill Semi-finish RP + BM RP - finish grinding VRM Mill 30.9 22.7 14.2 -  15.5 Roller press  - 4.4 9 15.5  - Auxiliaries + Fan 4.1 4.0 6.7 7.5 7.6 Total 35.0 31.1 29.9 23.0 23.1 We could see most of the MEA region grinding systems are CCBM.

6. 6 Finish Grinding Improved grinding (ball mills) High efficiency classifiers Energy management and process control General Measures Efficient fans with variable speed drives Optimization of compressed air systems Product & Feedstock Changes Reducing fineness of cement for selected uses Blended cements (i.e., Limestone, Pozzolana & Slag) Energy saving measures for sustainability Objectives Productivity: Maximum production with minimum power consumption Make a quality product: Control cement strength by Blaine Control setting time by gypsum and operational set-points. Control cement temperature .

7. 7 Mainly < 2 -5 % of energy input is required to break the particles. The major is lost as heat, noise, equipment wear & vibration. Heat generation typically estimated as ~25 Kcal/Kg of cement ground. Feed materials are not adequately cooled, the mill temperature could rise up to 140 o C and dehydrate gypsum and result in false set and undesirable coatings. So, the utilization of the available energy and precisely converting this into useful work is the key function of process. The Ball mill optimization exercise majorly involves 3 functions Understanding the mill charge ( Every 6 months) Mill sampling , Charge distribution & top ups . Air flow & diaphragm ( every 30-45 days) Mill venting, water spray, Diaphragm Study of Separator function ( every 3 months) Tromp, sep airflow, sep sealings. Grinding is intrinsically inefficient We are primarily focusing on the mill grinding chambers & separator for the performacne imporvement.

8. Grinding Performacne in the mill Chamber Closed circuit ball mill

9. 9 Size reduction along the mill. 1 st compartment : Coarse grinding 2 nd compartment : Fine grinding (Normal feed size 5%R on 25 mm & Top size 0.5%R on 35mm Mill Functionality Coarse Material grinding Fine material grinding Piece weight Impact force Specific surface Attrition force In general, Product Blaine of 4500 cm 2 /g in Ball mill: C-1 : Piece weight 1500 -1600 g/piece. C-2 :Specific surface 30-35 m 2 /t For Pre-grinding system : RP + BM C-1: 1100-1200 g/pc C-2: Specific surface 35-40 m 2 /t Large balls Small balls

10. 10 Maximum Ball size Quick evaluation : B =24 . √d 80 d 80 is the sieve size with 80% clinker passing

11. 11 Mill Basic requirements & parameters L/D Ratio: The optimum specific energy and the highest output for cement grinding is reached with an L/D ratio of 2.5 to 3.0 First compartment length equals 30 – 35% of total mill effective grinding length for 2 chamber mills. D i h f [%] h/D i Filling degree : It’s based on production needs to achieve lowest grinding energy, generally in the range of 28 - 32% depends on the mill diameter and design.

12. 12 Mill throughput assessment Using the mill outlet elevator Kw, approximate material flow could be estimated. Mill Throughput & Retention

13. 13 Mill power consumption Where: N = Mill Power Draw (kW) C = Mill Constant (0.514) = g x π / 60 g = Acceleration of gravity F = Ball Charge (MT) n = Mill Rotational Speed (rpm) µ = Torque Factor D = Mill Effective Diameter (m) a = Arm of Gravity in relation to mill diameter a =Distance between center of the mill and center gravity of charge. Mill Operating power N = C*F*n* μ *D*a Slegten's equation: Power, net = 0.0762 ( n ) 1.27 [ V n (1.36 - 1.2 V n ) L n ρ n ] D eff 3.014 where: where: V n Grinding Media fractional volume L n Compartment effective length (m) ρ n Grinding Media bulk density (t/m 3 ) D eff Compartment effective diameter (m) n Mill Speed (rpm) Rule of Thumb: One metric tonne of balls increases the mill power draw by 10 kW. Usually, 8 to 12 kWh/t is absorbed in the first compartment for clinker grinding (approximately 1/3 of the mill power DAWN Formula for the simple estimation: Net Power ( kW) = 0.2846 *D*A*W*N. D = Eff diameter (m) A = 1.073- Fractional volume % W = Ball charge (t) N = mill speed (rpm)

14. 14 Mill vent Air flow Air velocities for the mill ventilation Purpose: Forward movement of the material  retention time Take out fine particles and so diminish the risk of coating. Cooling of the material in mill  Diminish coating / dehydration of gypsum. Usual ranges of ventilation: Air speed in mill Open circuit : 0.8 to 1.2 m/s Closed circuit : 1.2 to 1.5 m/s Velocity effects: < 0.5 m/s : Tend to result inefficient over grinding and excessive heat generation with possible coating problem. > 1.4 m/s: Drag particle out of mill before they have been sufficiency ground

15. Separator Efficiency Improvement

16. 16 Tromp curve - Separator Efficiency Ideal Separator: No coarse in product and no fine in return /reject Short circuit /Delta = 0 Sharpness = 1.0 Separator Efficiency (V s ) V s = Actual energy saving/Max possible energy saving. The efficiency of the separator was established based on the energy saving in the mill by converting open circuit grinding to closed circuit with the maximum saving which may be achieved with the ideal separator.

17. 17 Separator Efficiency Drop Reduced separator efficiency leads to: Reduced mill production Increased mill motor power consumption Deterioration of product quality Methods to evaluate: Draw the Tromp curve for each cement type produced in the grinding system Correlate cement fineness, circulating load and separator bypass. Investigate impact of increase on separator efficiency on mill production: Benchmarking with other separators. Comparison with commissioning data.

18. 18 Probable causes that limit the separating efficiency The typical situations for 3 rd generation separators are: Uneven airflow and/or feed distribution to the rotor Reduced separating airflow due to: Separator fan damper (or speed) not at maximum Fan nominal too low Limited rotor speed due to mechanical problems or insufficient nominal capacity of the motor and/or gear box Contamination of the fines by coarse product Separator fines much finer than final product . Battery limits to consider: The bottleneck of the circuit is at the separator and not in the mill.

19. 19 Irregular airflow distribution to the rotor Uneven airflow distribution can be identified from: Observation of the ducting configuration: General arrangement Relative position inlet / outlet air ducts Uneven wear of paintings or steel along the guide vanes height Uneven wear of paintings or steel along the rotor blades height Low separator efficiency despite low material specific loads

20. 20 Symptoms Uneven airflow distribution can be identified and evaluated from: Airspeed mapping at the inlet of the separator volute Static pressure profile in each duct ( ) Fineness comparison of the fines at each cyclone (mass balance for each cyclone)

21. 21 Possible Solutions – flow distributions Even airflow distribution with air guide plates The positioning and length of the air guide plates should be done considering the air flow distribution in the ducting (start from where the air is already evenly distributed) Laminar and even flow across whole duct section Good Too short

22. 22 Uneven feed distribution to the rotor Symptoms Uneven wear of paintings or steel of the impact ring Uneven pressure loss and fineness in a cyclone air separator Separator efficiency is low in spite of low material specific loads Configuration of air slides from elevator discharge to the separator feed point(s)

23. 23 Possible solutions Uniform material load to all separator feeding points: Adjust / install splitter's Install mixing boxes Change air slides configuration

24. 24 Reduced separating airflow Symptoms: The circulating load and the bypass are high. Increases of the fresh feed rate to the mill leads to: significant increase of the bypass and the circulating load Too coarse final product The rotor is neither running at maximum speed, nor close to the installed power.

25. 25 Probable solutions Increase the airflow rate of the separator: Open the fan damper to the maximum (if variable speed fan, increase the speed to the maximum) Increase separator speed accordingly to keep the fineness Monitor impact on mill production Optimise power consumption by making trials with different separator airflows Replace the fan impeller (and/or fan drive ) to allow higher separator ventilation Evaluate impact of fan replacement on mill performance Fan nominal capacity can be changed after the replacement of the fan impeller by another one which does not have the same specifications. Bypass 1 Bypass 2 Bypass 1 > Bypass 2

26. Vertical Roller Mill for cement grinding

27. 27 Vertical roller mill for Cement Grinding 20 – 50% less power consumption than ball mill systems Suitable for Portland cement, Slag and Blended cements High productivity with stable, reliable operation Effective grinding when grinding blast furnace slag or blended cements with wet components Consistent cement quality with easy-to-adjust quality parameters .

28. 28 Vertical roller mill – PSD Modification Modification of PSD (particle size distribution) curve possible

29. 29 Vertical roller mill Optimization Specific Grinding Pressure: The specific grinding force for cement grinding is 900 - 1200 kN /m 2 Friction Factor: The torque or friction factor is the friction between material and the grinding surface. Table Speed: A variable speed drive may require to optimize for the different cement products and fineness. Optimum Dam Ring height is determined by trial and error Nozzle Ring air velocity will be in the range of 30 – 45 m/s Armour Ring angle shall be adjusted by trail and error method

30. 30 Key factor for stable operation Dust Load The mill outlet dust load to be maintained Mill Fan Flow The Fan flow to be maintained constant with the help of fan speed Mill Feed Rate The constant mill feed rate supports stable mill operation Slag is sticky in nature, which may create problem in feeding, Special lining and hot gas for slag to be provided in chutes and Rotary air Lock. Hydraulic Tensioning The N 2 and hydraulic pressure setting should be as per the supplier provided chart The nitrogen (N 2 ) pressure in the accumulator is to be checked on regular basis Mill Water Spray Mill water spray can be used during unstable bed thickness and vibration. False Air : The false air to be minimized to have proper gas velocity inside the mill .

31. 31 Variation in Operating Parameter – VRM Optimization Control (Increases) Layer thickness Differential pressure Mill Vibrations Main Motor Power Mill Exit Temp. Prod. Fineness Capacity Mill Feed Increase Increase Increase Increase Decrease Decrease Increase Grinding Pressure Decrease Decrease Increase Increase Decrease Increase Increase Water Injection No Change No Change Decrease Increase Decrease Increase No Change Separator Speed Increase Increase Increase Increase No Change Increase Decrease Mill Fan Speed Decrease Increase Increase Decrease Increase Decrease Decrease Nozzle Velocity Decrease Increase Increase Decrease Increase Decrease Decrease Dam Ring Height Increase Increase Decrease Increase No Change Decrease Decrease

32. 32 Vertical roller mill Particle size distribution Particle Size Distribution (PSD) of Product: Rosin-Rammler- Sperling-Bennet (RRSB). The RRSB distribution is a double logarithmic illustration of the Gauss distributions. The ideal Gaussian curves (PSDs normally distributed – valid for pure materials, like OPC, slag, limestone, etc.) convert into straight lines in the double logarithmic illustration of the RRSB diagram. The slope n is a measure for how narrow a particle size distribution is. The higher the slope n, the narrower the particle size distribution and vice versa.

33. 33 Typical slopes n in the RRSB diagram for different grinding systems

34. 34 Thank you for your attention www.mapei.ae